Introduce new command callback to shell.

This introduces a new feature of the IBinder command protocol
to allow the shell command implementation to call back into
its caller to ask it to open files in the calling context.  This
is needed so that commands that have arguments specifying files
can open those files as the calling shell, not the system (or
whatever) process.

Test: Manual

Change-Id: Idd5b49ea21057864cc9cef816b3e4afbf01948fc
diff --git a/libs/binder/Android.bp b/libs/binder/Android.bp
index 4780757..175e982 100644
--- a/libs/binder/Android.bp
+++ b/libs/binder/Android.bp
@@ -32,6 +32,7 @@
         "IProcessInfoService.cpp",
         "IResultReceiver.cpp",
         "IServiceManager.cpp",
+        "IShellCallback.cpp",
         "MemoryBase.cpp",
         "MemoryDealer.cpp",
         "MemoryHeapBase.cpp",